MATLAB Programming

2 Data Types
A(B)
ans =
5 15 30 35 50
In this case, the numeric values of array B designate the intended elements
of A.
Another type of array index, a logical index, designates the elements of A
based on their position in the indexing array, B. Inthismasking type of
operation, every true element in the indexing array is treated as a positional
index into the array being accessed.
Logical Indexing Example 1. This next example creates logical array B
that satisfies the condition A > 0.5, and uses the positions of ones in B to
index into A. Thisiscalledlogical indexing:
A = rand(5);
B = A > 0.5;
A(B) = 0
A =
0.2920 0.3567 0.1133 0 0.0595
0 0.4983 0 0.2009 0.0890
0.3358 0.4344 0 0.2731 0.2713
0 0 0 0 0.4091
0.0534 0 0 0 0.4740
A simpler way to express this is
A(A > 0.5) = 0
Logical Indexing Example 2. The next example highlights the location
of the prime numbers in a magic square using logical indexing to set the
nonprimes to 0:
A = magic(4)
A =
16 2 3 13
5 11 10 8
9 7 6 12
2-36